Pediatric Dosage Calculation Practice

The limit is stated per kilogram per day, so multiply it by the child's weight. 75 mg/kg/day × 24 kg = 1,800 mg in 24 hours. kg cancels, leaving mg per day. This is a daily ceiling, not a single dose. Before each dose, the nurse adds up all the acetaminophen given in the past 24 hours by every route, including oral combination products, and checks that the new dose keeps the total at or below 1,800 mg. The same 75 mg/kg limit works out to 3,750 mg at a weight of 50 kg, so this child's limit is far below that figure. Takeaway: a per-day limit in mg/kg is multiplied by the weight in kg and compared with the total of all doses in 24 hours.

Sources: Open RN Nursing Skills (ACC adaptation), 5.12 Safe Dosage Range; DailyMed: Acetaminophen injection label, Hikma (children 2 to 12 years: no more than 75 mg/kg in 24 hours, up to 3,750 mg, counting every route and product); DailyMed: Acetaminophen injection label, Baxter (children 2 to 12 years: no more than 75 mg/kg in 24 hours, up to 3,750 mg, counting every route and product)

The prescription is a daily amount per kilogram split into equal doses. The weight is already in kg, so no conversion is needed. Step 1: daily dose. 50 mg/kg/day × 15 kg = 750 mg/day. Step 2: number of doses. Every 6 hours is 24 ÷ 6 = 4 doses in 24 hours. Step 3: single dose. 750 mg ÷ 4 doses = 187.5 mg. Giving the 750 mg daily total as one dose would be 4 times too much. Dividing by 6, the hours between doses, instead of by the 4 doses gives 125 mg, which is too little. The prescription matches the label dose for a child under 40 kg with a genitourinary infection: 50 mg/kg/day in equally divided doses every 6 to 8 hours. Takeaway: for mg/kg/day in divided doses, multiply by the weight in kg to get the daily amount, then divide by the number of doses in 24 hours; every 6 hours is 4 doses.

Sources: Open RN Nursing Skills (ACC adaptation), 5.12 Safe Dosage Range; Open RN Nursing Skills (ACC adaptation), 5.11 Weight-Based Calculations; DailyMed: Ampicillin for Injection label (under 40 kg, gastrointestinal and genitourinary infections: 50 mg/kg/day in equally divided doses every 6 to 8 hours)

Step 1: top of the daily range. 7.5 mg/kg/day × 20 kg = 150 mg/day. Step 2: every 8 hours is 3 doses, so the highest single dose is 150 mg ÷ 3 = 50 mg. The bottom of the range is 6 mg/kg/day × 20 kg = 120 mg/day, or 40 mg per dose, so the safe single dose is 40 to 50 mg. The prescribed 45 mg lies inside it, and the dose can be given. Recording 150 mg confuses the daily limit with a single dose. Takeaway: a single dose is checked against a per-dose range, so divide the per-day limits by the number of doses first.

Sources: Open RN Nursing Skills (ACC adaptation), 5.12 Safe Dosage Range; DailyMed: Gentamicin injection (pediatric) label, dosage section (children 6 to 7.5 mg/kg/day, given as 2 to 2.5 mg/kg every 8 hours)

Step 1: daily dose. 45 mg/kg/day × 6.8 kg = 306 mg/day. Step 2: single dose. 306 mg ÷ 2 doses = 153 mg, given every 12 hours. Step 3: volume. (153 mg ÷ 200 mg) × 5 mL = 3.825 mL. Round once, at the end: a volume of 1 mL or more goes to the nearest tenth, so 3.8 mL. Using the daily 306 mg as the single dose would double what the infant receives, and leaving out the × 5 mL gives 0.77 mL, about a fifth of the dose. Takeaway: for a daily dose in divided doses, work in order: mg per day, mg per dose, then mL per dose.

Sources: Open RN Nursing Skills (ACC adaptation), 5.12 Safe Dosage Range; Open RN Nursing Skills (ACC adaptation), 5.11 Weight-Based Calculations; Open RN Nursing Skills (ACC adaptation), 5.5 Rounding; DailyMed: Amoxicillin for oral suspension label, 200 mg/5 mL and 400 mg/5 mL (children older than 3 months: 45 mg/kg/day in divided doses every 12 hours)

Children's weights are recorded in kilograms only, so the nurse converts the charted pounds and confirms the kg weight. Step 1: weight. 37 lb ÷ 2.2 = 16.818 kg, rounded to 16.8 kg. Step 2: prescribed per day. Every 6 hours is 4 doses, so 250 mg × 4 = 1,000 mg/day. Step 3: dose per kg. 1,000 mg/day ÷ 16.8 kg = 59.52, rounded to 59.5 mg/kg/day. The nurse compares this result with the range listed for the infection being treated. It is above the top of that range: in mg, the range for this child is 25 × 16.8 = 420 mg/day to 50 × 16.8 = 840 mg/day, and 1,000 mg/day is more than that. Cephalexin has a higher range, 50 to 100 mg/kg/day, for severe infections, so the dose may be what the primary health care provider intends. The nurse does not guess, and clarifies the prescription with the primary health care provider before giving the dose. Takeaway: find the weight in kg, the daily total and the mg/kg/day, then compare with the range for the indication; a dose outside that range is clarified before it is given.

Sources: Open RN Nursing Skills (ACC adaptation), 5.12 Safe Dosage Range; Open RN Nursing Skills (ACC adaptation), 5.4 Equivalencies; DailyMed: Cephalexin for oral suspension label (children: usual 25 to 50 mg/kg/day in equally divided doses; severe infections 50 to 100 mg/kg/day); Open RN Nursing Skills (LibreTexts), 15.2 Basic Concepts of Administering Medications (right dose: check the range for the client's age and condition; clarify with the prescriber before giving); Open RN Nursing Health Promotion, Chapter 14: Planning Care for the Ill Child (dose by weight; weigh the child and record the weight in kilograms only)